In the event of industrially manufacturing labels, a production method in which a hot melt adhesive is melted, the molten hot melt adhesive is applied on a substrate such as a releasing paper by a coating apparatus such as a die coater, and an adhesive sheet thus obtained is processed into products having a constant size by cutting the adhesive sheet using a die cutter, is usually employed.
In this production method, the productivity of labels depends largely on the properties of the hot melt adhesive used, and particularly, the effect of the application temperature and die cutting properties (ease of cutting to a constant size without threading or adhering to the die when the adhesive is cut with a die cutter) of the hot melt adhesive on the productivity of labels has grown extremely large.
Accordingly, investigations have been conducted on hot melt adhesives that are used in the manufacture of labels, so as to improve the die cutting properties, to lower the appliable temperature, and the like. For example, Patent Literature 1 describes that when a tackifier resin is incorporated into two kinds of elastomers respectively having a particular relationship between glass transition temperatures and tan δ values in the measurement of dynamic viscoelasticity, a pressure sensitive adhesive having excellent die cutting properties and excellent adhesive performance is obtained. Furthermore, Patent Literature 2 discloses a pressure sensitive adhesive prepared by mixing a styrene-isoprene-styrene block copolymer with a tackifier and a styrene-isoprene block copolymer. In this pressure sensitive adhesive, the incorporation of the styrene-isoprene block copolymer contributes to an increase in the tan δ value at 20° C. of the pressure sensitive adhesive, and as a result, the die cutting properties are enhanced. Furthermore, the adhesive performance such as adhesive strength or the heat resistance of adhesion is also improved.
However, it has been difficult to say that even such hot melt adhesives have a satisfactory balance between the ease of coating at a relatively low temperature and the die cutting properties. Therefore, there has been a demand for a hot melt adhesive for labels which can achieve a high-level balance between the ease of coating at a relatively low temperature and the die cutting properties.